“This is the day you’ve waited for,” he says. “Today is the day you’ve dreamed of . . . that moment has arrived . . . that run down the streets broad and narrow that you’ll never forget.” Many of his congregation are stretching. Queuing for portaloos. Enthusiastically greeting friends and hugging family members.

Some, the lunatics, are engaged in pre-race running (sprinting up and down).

One man, more sensibly, is having a pre-race cigarette. Does that help? “It steadies me,” chuckles Armagh man Wayne Lavery. He and his friend Eamon Lavery (no relation) are dressed in white hooded bodysuits. “We’re the forensics team,” says Wayne.

“Actually it’s just to keep us warm,” says Eamon.

A group walks by wearing what look like large single butterfly wings with numbers inscribed on them. These are the pacesetters – those brave metronomic souls against whom weary joggers can pace themselves.

There are also some people in fancy dress – leprechauns, teenage mutant ninja turtles . . . and Batman. Not Bruce Wayne, but Dubliner Barry Cassidy. “I’ve run six marathons,” he explains. “I thought this year I’d do something different . . . for Halloween.”

“What do you think of this?”

I ask his fiancée, Niamh Murphy, who’s there for moral support.

“Well, it’s different,” she says, sounding a little unsure.

Many are representing charities and causes. “I’m running so Jack can walk,” reads one T-shirt. “Running for Jesus,” reads another. “Clowns for Haiti,” reads the running shirt of, well, a clown. A quartet are wearing shirts with a photo of a friend and the words “Feargal 1962 – 2012”.

“Go on, Fiona!” reads the homemade glittery sign held by James O’Connell. “That’s our daughter,” explains his wife Elizabeth. “She’s running to raise money for leukaemia. My sister lost her husband, Michael Walsh, in January. He was a great sportsman and Fiona’s doing this in memory of him.”

“We’ve told her whenever she feels like stopping to stop,” says her sister, Latisha Walsh. “But she’s been preparing for a long time. We’re very proud of her.”

At this point, the massing runners begin divesting themselves of tracksuit tops and extra layers by just firing them overhead to the side of the road.

It looks like weird confetti. Later volunteers collect this clothing in big green containers for St Vincent de Paul.

Claire Messitt, the grandniece of recently deceased Irish Olympian Bertie Messitt, is running in his honour. Her parents, Phyllis and Ivan Messitt, are holding up homemade, heart-shaped signs egging her on. Bertie has been an inspiration to them all.

“He never talked about his career,” says Phyllis. “But in one week back in the 1960s he won a bronze medal in the world championships and broke the Irish record and a world record.” The Messitts have been involved with running and the Dublin Marathon since its inception. “I’ve run 19 marathons,” says Ivan.

And Phyllis? “I stayed at home and minded four children while he ran 100 miles a week.” She laughs. “It’s a wonder we’re still here talking.”

Soon we hear the “beautiful sound” (Dave Dempsey’s words) of the first starter pistol and 14,300 people run by. The difference between the fresh faces and sturdy limbs at the start of a marathon and the flushed and staggering runners at the finish, is quite striking.

Even more so after the “elite” athletes have come in, headed by Kenyan runner Geofrey Ndungu (winning for the second time).

There’s a lot more vomiting involved in completing a marathon than I anticipated. It’s often joyous vomiting, but vomiting nonetheless.

“Hurray! Bloody brilliant!” says one successful runner, before casually vomiting and then resuming his celebration arm-in-arm with a friend.

Some finish the race with their arms around one another. Some are joined by their children for the last hundred metres. Some collapse as soon as they cross the line. A few need wheelchairs. Many lean against the railings looking absolutely destroyed. A few, the lunatics, continue running after they’ve crossed the finish line.

Many, rather hearteningly, are assisted over the line by selfless friends and relatives. One man is carried across by stewards, his legs gone from beneath him.

Gary Crossan, on the other hand, arrives pushing a tiny infant in a buggy (it’s presumably his own infant). “There are too many kids sitting in front of computers,” he explains.

Fintan and Barbara Coughlan almost burst with pride as their son Garrett heads towards the finish line in the first batch. He works as a physiotherapist for the IRFU and has run all his life. “When he was four years of age we were going to Donegal on a holiday,” says Barbara. “We stopped the car and in a field there was a local race. Garrett said ‘Can I run in that’. He did and he won!”

This year Garrett is running to raise money for a cancer charity in honour of his brother Dillon, who died last year. Tears well up as they say this but the sadness is mixed with absolute pride in Garrett. “He’s never given us an ounce of trouble,” says Barbara.

Many are running in memory of passed family members and friends. “I’m running in memory of my daughter,” reads one man’s T-shirt.

Carlow-born New York resident Mary Nolan is running in memory of her sister, Margaret McGee, who died two years ago. Mary first ran the New York marathon last year on what would have been her sister’s 48th birthday.

She’s over the finish line now, waiting for her other sister, Theresa. “Margaret’s memory 100 per cent motivates me,” she says. “She was a great fitness person herself and she inspired all of us.” Running a marathon, she says, is far from a lonely experience. “Training can be lonely, but this? This is amazing.”

She’s right. I’m a bit overwhelmed and I’m not even participating (I’m out of breath just typing this).

For most people the marathon isn’t about individualistic competition, but personal achievement, community, family, friendship and the memory of lost loved ones.

At the finish line people are physically aching, blistered, bleeding, staggering, vomiting, walking arm-in-arm and beaming with happiness.

“It’s one of the best moments of my life,” says Kevin Baker of the Mullingar Harriers. He’s shivering in a silver blanket as he waits for his brother to cross the line.

The Dublin Marathon. It’s not pretty, but it’s oddly beautiful.

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